Document falsification and product counterfeiting are significant problems that have been addressed in a variety of ways. One of the more successful approaches has been the use of latent or hidden images applied to or printed on objects to be protected. These images are generally not viewable without the assistance of specialized devices that render them visible.
One approach to the formation of a latent image is to optically encode the image so that, when applied to an object, the image can be viewed through the use of a corresponding decoding device. Such images may be used on virtually any form of printed document including legal documents, identification cards and papers, labels, currency, stamps, etc. They may also be applied to goods or packaging for goods subject to counterfeiting.
Objects to which an encoded image is applied may be authenticated by decoding the encoded image and comparing the decoded image to an expected authentication image. The authentication image may include information specific to the object being authenticated or information relating to a group of similar objects (e.g., products produced by a particular manufacturer or facility). Production and application of encoded images may be controlled so that they cannot easily be duplicated. Further, the encoded image may be configured so that tampering with the information on the document or label is readily apparent.
Authentication of documents and other objects “in the field” has typically required the use of separate decoders such as lenticular or micro-array lenses that optically decode the encoded images. These lenses may have optical characteristics that correspond to the parameters used to encode and apply the authentication image and may be properly oriented in order for the user to decode and view the image. The decoding lenses may also be able to separate secondary images from the encoded images. For example, the decoding lens can be a lenticular lens having lenticules that follow a straight line pattern, wavy line pattern, zigzag pattern, concentric rings pattern, cross-line pattern, aligned dot pattern, offset dot pattern, grad frequency pattern, target pattern, herring pattern or any other pattern. Other decoding lenses include fly's eye lenses and any other lens having a multidimensional pattern of lens elements. The elements of such lenses can be arranged using a straight line pattern, square pattern, shifted square pattern, honey-comb pattern, wavy line pattern, zigzag pattern, concentric rings pattern, cross-line pattern, aligned dot pattern, offset dot pattern, grad frequency pattern, target pattern, herring pattern or any other pattern. Examples of some of these decoding lenses are illustrated in FIG. 1.
In some cases, lens element patterns and shapes may be so complex that it they are impossible or impractical to manufacture. While such patterns may be highly desirable from the standpoint of their anti-counterfeiting effectiveness, cost and technology difficulty in their manufacture may limit their use.